Abstract: A spray gun suitable for spraying plaster and other particulate matter uses a series of easily replaceable elements for fast cleaning and changeover of the spray gun. A barrel portion of the gun has a supply chamber for receiving material to be sprayed. A slidable tube is mounted in the barrel portion and provides a jet of compressed air for forcing the material to be sprayed through a nozzle plate. A handle portion extends downwardly from the gun and supports a slidable trigger mechanism. The trigger mechanism includes a fixed member at one end thereof which is slidable on the slide tube trapped between an adjustable stop member and a further member secured on the slide tube. The adjustable stop member can also be used to position the slide tube for continuous operation independent of the trigger mechanism. The adjustable stop member is moved along the slide tube until it contacts the end of the barrel. Further movement moves the slide tube rearwardly and is held in the open position.